Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Applications for fuel cells include battery replacement, mini and microelectronics, car engines, power plants, and many others. One advantage of fuel cells is that they are substantially pollution-free.
In hydrogen fuel cells, hydrogen gas is oxidized to form water, with a useful electrical current produced as a byproduct of the oxidation reaction. A solid polymer membrane electrolyte layer may be used to separate the hydrogen fuel from the oxygen. The anode and cathode are arranged on opposite faces of the membrane. Electron flow between the anode and cathode layers of the membrane electrode assembly may be exploited to provide electrical power. Hydrogen fuel cells are impractical for many applications, however, because of difficulties related to storing and handling hydrogen gas.
Organic fuel cells may prove useful in many applications as an alternative to hydrogen fuel cells. In an organic fuel cell, an organic fuel such as methanol is oxidized to carbon dioxide at an anode, while air or oxygen is simultaneously reduced to water at a cathode. One advantage over hydrogen fuel cells is that organic/air fuel cells may be operated with a liquid organic fuel. This eliminates problems associated with hydrogen gas handling and storage. Some organic fuel cells require initial conversion of the organic fuel to hydrogen gas by a reformer. These are referred to as “indirect” fuel cells. The need for a reformer increases cell size, cost, complexity, and start up time. Other types of organic fuel cells, called “direct,” eliminate these disadvantages by directly oxidizing the organic fuel without conversion to hydrogen gas. Further classification of fuel cells may distinguish “passive” cells from “active” cells. In an active cell, fuel solution is continuously supplied for contact with the anode (as by pumping, for example), whereas in a “passive” cell a specified quantity of fuel solution is provided for reaction.
Fuel cells including methanol, formic acid, and other organic fuel cells make use of an anode catalyst and a cathode catalyst to promote efficiency. The catalysts promote the reduction reaction at the cathode and the oxidation at the anode. Some prior efforts have focused on platinum (Pt) based catalysts, with platinum/ruthenium or platinum/palladium anode catalysts being two examples. When used in an organic fuel cell, known anode catalysts, including Pt based catalysts, have only a low level of activity as compared to those in a hydrogen fuel cell. As a result, organic cells tend to require relatively large loadings of the catalyst. This adds considerable cost to the fuel cells due to the high price of the precious and semi-precious metals in the catalysts.